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p.2 #4 · 35mm side by side review posted | |
pdmphoto wrote:
Nice work, but again the definition of "borders" seems to cloud the results. I've tried about half of the listed lenses and my corner results don't match these border results, so I'd be careful about interpretting the results from the "borders".
Valid question - take a look at the targets displayed in FAQ. MTF is measured off left top and right bottom slanted squares. These are 85% distance from the center (for self-assembled chart) and 80% distance from the center (for the iso chart).
pdmphoto wrote:
Besides the "borders" issue. I am at a loss to understand how these tests can be so different from my own real world tests. I'm sure it is a combination of factors, but I wonder if these tests are done at a distance considerably less than infinity? I've found some lenses do very well at distances close in, but progressively worse towards infinity. If that is the case than these tests are more close focus, than real world performance for the type of photography I do.
I think I have mentioned this in my other posts and it should definitely be in the FAQ. I record best MTF, meaning that I don't take one set at just a particular distance, but rather vary the distance to the chart as well to measure MTF at various distances. Thus one lens might be optimized for closeups while the other will be optimized for infinity - I will have the best MTF for both. I do not record at what distance the lens produced the best MTFs - just the best MTF out of all sequences. The process is relatively streightforward, it just requires bunch of measurements - start at a distance, go through focus brackets for all tested apertures, move the camera/lens by 1m, repeat, move by 1m, repeat etc...
This is all described in the FAQ section - specifically put it there since I was repeatedly getting this question.
Edited by eosslr on May 12, 2008 at 11:00 PM GMT
Edited on May 12, 2008 at 11:00 PM
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